‘Bio ghost’ of mighty mouse reveals important colourful discovery

A false colour image of ‘mighty mouse’. Blue represents calcium in the bones, green is the element zinc (shown to be important in the biochemistry of red pigment) and red is an organic sulphur. Image: Nature Communications

For the first time, researchers have discovered red pigment in an ancient fossilised mouse, shining a light on what the creature looked like.

Imaging technology has advanced to the point that we can now see the faint traces of colour in creatures dating back millions of years ago. In a paper published to Nature Communications, a team of international researchers led by the University of Manchester has announced the first evidence of red pigment in an ancient fossil.

Located in what is now the German village of Willershausen, the exceptionally well-preserved mouse – similar to today’s field mouse – would have roamed the land approximately 3m years ago. The creature, affectionately named ‘mighty mouse’, was once dressed in a reddish fur on its back and sides, and had a white tummy.

The revealing of its colour scheme was thanks to x-ray spectrometry and multiple imaging techniques to detect the delicate chemical signature of the mouse’s pigments.

“Where once we saw simply minerals, now we gently unpick the ‘biochemical ghosts’ of long-extinct species,” said Phil Manning, co-lead of the study.

Until recently, techniques used to study fossils weren’t capable of looking at their pigmentation, leaving out an important part of the investigation into what an ancient creature might have looked like.

The fossilised remains of ‘mighty mouse’. Image: University of Göttingen

It’s all about chemistry

This most recent breakthrough, however, maps key elements associated with the pigment melanin, the dominant pigment found in animals. In the form of eumelanin the pigment gives a black or dark brown colour, but in the form of pheomelanin it produces a reddish or yellow colour.

Up until now, researchers have focused on eumelanin, previously used to reveal dark and light patterns in the feathers of the first birds, including the famous link between dinosaurs and birds, Archaeopteryx.

Previous work undertaken by one of the research team – Nick Edwards of the SLAC National Accelerator Lab in the US – showed it was possible to differentiate between eumelanin and pheomelanin, setting a chemical benchmark for this most recent paper and the discovery of the red pigment.

“We had to build up a strong foundation using modern animal tissue before we could apply the technique to these ancient animals,” Edwards said. “It was really a tipping point in using chemical signatures to crack the colouring of ancient animals with soft-tissue fossils.”

Trace metals found in pigments were uncovered during the scans and were incorporated in the fossilised mouse fur in exactly the same way that they bond to pigments in animals with high concentrations of red pigment in their tissue.

Co-lead of the study, Roy Wogelius, said: “Our hope is that these results will mean that we can become more confident in reconstructing extinct animals and thereby add another dimension to the study of evolution.”